Mouth Rot: symptoms, treatment, prevention
Mouth Rot is a localised oral form of Columnaris caused by Flavobacterium columnare; it progresses rapidly in bettas and gouramis and can become systemic.
Overview
Mouth Rot is a localised oral form of Columnaris caused by Flavobacterium columnare, a Gram-negative bacterium. It is often misidentified as a fungal infection because the lesions look cottony. The disease progresses rapidly, especially in bettas and gouramis, and untreated cases can be fatal.
Symptoms
- White cottony patch on mouth or lips
- Frayed mouth tissue
- Difficulty closing the mouth
- Anorexia
- Rapid weight loss
- Secondary fin rot
Causes
Triggers include high temperatures, poor water quality, overcrowding and stress. Flavobacterium columnare thrives in warm, organically loaded water, so summer outbreaks are common.
Diagnosis
A cotton-like white lesion on the lips that progresses quickly and is centered on the mouth area is characteristic. Differentiate from true fungus (rare without prior injury) and from bacterial body lesions — Columnaris classically follows fin and mouth margins.
Treatment
Move affected fish to a hospital tank and combine salt with a targeted antibiotic; lower temperature slightly because Flavobacterium columnare is more aggressive in warm water.
Quarantine
Use a bare-bottom hospital tank with strong filtration and a heater. Disinfect nets and equipment from the original tank before reusing them.
Medication
- Aquarium salt (NaCl) at about 1 g per litre in the hospital tank for 7-10 days.
- Kanamycin sulfate in food or water for 7-10 days; lower temperature to about 24 °C if the species tolerates it.
Recovery
After lesions resolve, continue large water changes and a varied diet; damaged mouth tissue regenerates over weeks. Avoid pushing the temperature above 28 °C in recovering bettas.
Prevention
- Avoid temperatures above 28 °C in bettas if any history of mouth rot
- Good water flow
- Avoid overstocking
- Varied high-quality diet